This invention relates to the improvement on spherical bodies of carbon or graphite which are used as industrial machine parts.
As is well known, the spherical bodies of carbon or graphite used as sliding members, etc., in industrial machines have many advantages such as light weight and compactness, low frictional properties, splendid wear resistance and thermal dimensional stability over steel and plastic spherical bodies.
Conventional spherical bodies of carbon or graphite are formed by cutting and polishing carbon materials which have been obtained by (1) kneading with heating a raw material such as coke, carbon black, natural graphite, artificial graphite, etc., with a binder such as tar, pitch, etc., molding under pressure the resulting mixture, followed by heat treatment or baking, if necessary further graphitization, or (2) gradually heating in an oxidizing atmosphere a cured material of thermosetting resin such as a phenolic resin, furan resin or the like alone or pitch containing a large amount of aromatic components to give non-melted pitch alone, molding the cured material of thermosetting resin or the non-melted pitch under pressure, followed by heat treatment (baking and if necessary graphitization). The carbon material obtained by the process (1) exhibits a high degree of anisotropy in material strength and that obtained by the process (2) is so-called vitreous carbon which has fine crosslinking and hardly brings about the growth of graphite crystals even if subjected to graphitization treatment, so that it cannot be sufficient in thermal conductivity. Also, in practical use of the spherical bodies made from said carbon materials as bearings for instance, when a part of the spherical body is exposed to severe conditions such as rapid heating or quenching, the surface of the spherical body would suffer from "pitting" or the spherical body itself would develop cracks due to a difference in thermal expansion between the surface and inside portion of the spherical body, resulting in a short service life of the spherical body.